It is known from U.S. Pat. No. 4,451,442 to contact fluid streams containing hydrogen sulfide from a steam turbine or from a sour gas stream with an aqueous solution of a polyvalent metal chelate and an oxidizing agent whereby the hydrogen sulfide is converted to free sulfur and then to soluble sulfur compounds, and wherein the metal chelate is reduced to a lower oxidation state metal chelate and the reduced metal chelate is subsequently oxidized with air back to the higher oxidation state and reused.
It is known from U.S. Pat. No. 3,859,414 to remove H.sub.2 S from a gas stream containing H.sub.2 S and CO.sub.2 without essentially affecting the CO.sub.2 content of the gas stream by contacting the gas stream, in an absorption zone, with an aqueous absorbent stream containing a water-soluble sulfite compound at thiosulfate production conditions, including a pH selected from the range of about 6 to about 7 and selected to form a treated gas stream substantially reduced in H.sub.2 S content and a rich absorbent stream which contains a thiosulfate compound and which is substantially free of elemental sulfur.
It is known from U.S. Pat. No. 3,446,595 to contact hydrogen sulfide with bisulfite to form a mixture of elemental sulfur and sodium sulfite solution, to separate the elemental sulfur from the sulfite solution, and to regenerate the sulfite solution with sulfur dioxide which is obtained by combustion of a portion of the recovered elemental sulfur. This process requires the presence of bisulfite for hydrogen sulfide treatment and sodium hydroxide and sodium carbonate are disclosed as suitable makeup solutions for the contact step.
It is known from U.S. Pat. No. 4,629,608 to use cationic polymeric catalysts in an aqueous metal chelating solution for removing H.sub.2 S from the exhaust steam in a geothermal power plant.
The combustion of H.sub.2 S and subsequent absorption of the resulting sulfur dioxide in a caustic solution is described in the prior art, for example, in U.S. Pat. Nos. 4,310,438; 4,342,733; 3,447,903; and U.S. Pat. No. 4,622,212.